1. Field of the Invention
The present invention relates to a semiconductor forming technology by plasma CVD (such as capacitively-coupled CVD), and more specifically to a method of forming a minute low-temperature oxide film and a multilayer resist method utilizing the same with respect to a substrate containing thermally unstable substances.
2. Description of the Related Art
Integrated semiconductor circuits have become increasingly minute to achieve higher speed and functionality. To produce minute circuits, demands for photolithography, dry-etching and other minute processing technologies are growing stronger. Applications utilizing the multilayer resist method are expanding to address the trends of shorter exposure wavelength, increasing height gaps on the base substrate surface, and so on (one such example is found in Japanese Patent Laid-open No. 7-181688).
Under the multilayer resist method, a film is formed on a substrate on which the bottom-layer resist is already applied, which limits the maximum temperature permitted during the forming of the intermediate layer by the thermal limitations of the bottom-layer resist. Various films have been examined for use as the intermediate layer in a multilayer resist structure. Among others, SOG (Spin On Glass) films (coated films) exhibit low minuteness and poor ashing resistance (the process of coating and baking results in low density), and therefore are unable to fully function as a mask when the bottom-layer resist pattern is formed. Intermediate layers formed by high-density plasma apparatuses, such as ECR plasma processing apparatuses, offer excellent minuteness but these films cause semiconductor elements to suffer plasma damage during the film forming process (due to high density). In addition, use of SOG films and high-density plasma apparatuses results in low productivity (due to the many processing steps required by SOG films and the slow deposition speeds of high-density plasma apparatuses) and high production cost (due to the high costs of SOG materials and high prices associate with high-density plasma apparatuses).